Embedded burst demodulation and tracking error generation

Abstract

A disk drive comprising circular data tracks divided into sectors each of which includes a data field and a servo field containing embedded servo signals, an embedded signal sensor for sensing embedded servo signals on a data surface and a head positioning system for positioning a read/write head over a selected data track. The servo fields in the data tracks contain first and second embedded servo signals of substantially constant amplitude high-frequency bursts offset relative to each other and disposed on alternate sides of the track centerlines. The sensed signals corresponding to the first and second embedded servo signals are sampled and compared to provide a track error signal for positioning the read/write head over a selected data track.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. In a disk drive incorporating a disk assembly comprising at least one data surface having circular data tracks containing sectors each of which includes a data field and a servo field providing embedded servo signals, a sensor for sensing said embedded servo signals and a head positioning system for positioning said sensor over a selected data track, the embedded servo signals in each servo field comprising first and second substantially constant amplitude high-frequency bursts consisting of transitions of alternating polarity, and said first and second bursts being disposed on opposite sides of the centerline of the track containing them and offset relative to each other in the circumferential direction, a circuit for providing an embedded track error signal to which said head positioning system responds, said track error signal generating circuit comprising: A) a rectifier connected to rectify the sensed servo signals to provide a rectified signal output;   B) a resettable integrator connected to separately integrated the rectified output corresponding to each of said bursts to provide servo signal outputs corresponding to the strengths of the sensed servo signals;   C) means for sampling the servo signal outputs corresponding to each of said bursts; and   D) means for comparing the sampled outputs from the bursts on one side of the track centerline with the sampled outputs from the bursts on the other side of the centerline to provide said track error signal.   
     
     
       2. The track error signal generating circuit of claim 1 further comprising a bandpass filter connected between the servo signal sensor and the rectifier to pass signals at said high frequency. 
     
     
       3. The track error signal generating circuit of claim 2 in which a square-wave generator is connected to provide the sole input to the bandpass filter to sense zero offset in the track error signal generating circuit. 
     
     
       4. The track error signal generating circuit of claim 1 wherein the sampling means comprises sample-and-hold circuits activated and reset according to timing signals corresponding to the expected sensing of embedded track error signals and the integrator is enabled and reset according to said timing signals. 
     
     
       5. In a disk drive incorporating a disk assembly comprising at least one data surface having circular data tracks containing sectors each of which includes a data field and a servo field providing embedded servo signals, a sensor for sensing said embedded servo signals and a head positioning system for positioning a read/write head over a selected data track, the embedded servo signals in each servo field comprising first and second substantially constant amplitude high-frequency bursts consisting of transitions of alternating polarity, and said first and second bursts being disposed on opposite sides of the centerline of the track containing them and being offset relative to each other in the circumferential direction, a circuit for generating an embedded track error signal to which said head positioning system responds, said track error signal generating circuit comprising: A) a rectifier connected to rectify the sensed servo signals to provide a rectified signal output;   B) a low-pass filter connected to smooth the rectified output corresponding to each of said bursts to provide servo signal outputs corresponding to the strengths of the sensed servo signals;   C) means for sampling the servo signal outputs corresponding to each of said bursts; and   D) means for comparing said sampled outputs from the bursts on one side of the track centerline with the sampled outputs from the bursts on the other side of the centerline to provide said track error signal.   
     
     
       6. The track error signal generating circuit of claim 5 further comprising a bandpass filter connected between the servo signal sensor and the rectifier to pass signals at said high frequency. 
     
     
       7. The track error signal generating circuit of claim 6 in which a square-wave generator is connected to provide the sole input to the bandpass filter to sense zero offset in the track error signal generating circuit. 
     
     
       8. The track error signal generating circuit of claim 5 wherein the sampling means comprises sample-and-hold circuits activated and reset according to timing signals corresponding to the expected sensing of embedded track error signals. 
     
     
       9. For a disk drive incorporating a disk assembly comprising at least one data surface having circular data tracks containing sectors each of which includes a data field and a servo field providing embedded servo signals, a sensor for sensing said embedded servo signals and a head positioning system for positioning said sensor over a selected data track, the embedded servo signals in each servo field comprising first and second substantially constant amplitude high-frequency bursts consisting of transitions of alternating polarity, and said first and second bursts being disposed on opposite sides of the centerline of the track containing them and offset relative to each other in the circumferential direction, a method for providing an embedded track error signal to which said head positioning system respond, said method comprising: A) rectifying the sensed servo signals to provide a rectified signal output;   B) smoothing the rectified output corresponding to each of said bursts to provide servo signals outputs corresponding to the strengths of the sensed servo signals;   C) sampling the servo signal outputs corresponding to each of said bursts; and   D) comparing the sampled outputs from the bursts on one side of the track centerline with the sampled outputs from the bursts on the other side of the centerline to provide said track error signal.   
     
     
       10. The method of claim 9 further comprising the step of calibration using a constant amplitude square as the servo signal input to determine zero offset.